Ignition of propellants/explosives from a remote control point has been accomplished by a centercore system in which a single ignitor tube is located in the center of the explosive charge. A pulse of electric current is passed through a bridge wire so as to cause the wire to vaporize and ignite a pyrotechnic contained within an end of the tube. This ignites an adjacent black powder primer which in turn ignites ignitor strands extending throughout the length of the tube. Because the tube is strong enough to initially contain the pressure resulting from the hot gases generated during the ignition, they are forced out of vent holes along the tube in the form of jets so as to penetrate the explosive charge and ignite it.
Because the rate of this penetration is limited, only about half of the material in the ignitor strands and about 50% of the propellant/explosive charge are burned when the projectile is expelled. This inefficient use of material is costly, but, in addition, the fact that the amount of the charge ignited varies has adverse functional effects. Thus, if charges are used to propel projectiles, the initial velocities are different so as to affect the ballistics, and if they are used in blasting rock, the forces created vary from charge to charge. Furthermore, the slow and uneven spread of ignition of the charge can create standing pressure waves having dangerous effects, e.g., it can blow the breech of a gun.
Attempts have been made to solve these problems through modifying the centercore system. The vent holes in the ignition tube have been positioned farther from the pyrotechnic end, and forward venting tips have been used, but the improvements have been marginal. In addition, an electrically operated system such as just described is subject to inadvertent initiation from electromagnetic radiation, spurious electrical signals and static discharges. Furthermore, it has been reported that elimination of the bridgewire would eliminate at least 80% of the test procedures required to ensure safety.